Modulation of Ferroelectric and Optical Properties of La/Co-Doped KNbO3 Ceramics

The phase transition, microscopic morphology and optical and ferroelectric properties are studied in a series of La- and Co-doped KNbO3-based ceramics. The results show that the doping induces the transformation from the orthorhombic to the cubic phase of KNbO3, significantly reduces the optical bandgap and simultaneously evidently improves the leakage, with a slight weakening of ferroelectric polarization. Further analysis reveals that (i) the Co doping is responsible for the obvious reduction of the bandgap, whereas it is reversed for the La doping; (ii) the slight deterioration of ferroelectricity is due to the doping-induced remarkable extrinsic defect levels and intrinsic oxygen vacancies; and (iii) the La doping can optimize the defect levels and inhibit the leakage. This investigation should both provide novel insight for exploring the bandgap engineering and ferroelectric properties of KNbO3, and suggest its potential applications, e.g., photovoltaic and multifunctional materials.

An Autosomal Dominant SCID Form Due to a Gain of Function Mutation in the RAC2 Gene

Severe combined immunodeficiencies (SCIDs) form a heterogeneous group of life-threatening genetic disorders defined by the absence of autologous T cells and an intrinsic or extrinsic defect in the B-cell compartment. In our cohort, three newborn patients with bone-marrow hypoplasia associated with clinical and biological features of SCID received allogenic hematopoietic stem cell transplantation in the first weeks of life. To identify the molecular defect involved in this life threatening SCID form, we performed whole-genome sequencing on patient's fibroblasts. The same heterozygous, dominant missense mutation was found in the RAC2gene encoding for the RAC2 GTPase (p.G12R). By biochemical analyses we demonstrated that arginine substitution at position 12 leads to sustained activation of the RAC2 signalling pathway; the G12R mutation is therefore a gain of function mutation. In cord blood hematopoietic cells, we observed that the mutation disrupts mitochondrial activity and blocks hematopoietic stem/progenitor cells (HSPCs) differentiation toward the myeloid and lymphoid lineages. Altogether, our data emphasize the involvement of the RAC2 signalling pathway during hematopoeisis and might thus explain the severity of the patients' clinical and immunological phenotype. The present study is the first to report an autosomal dominant form of SCID and suggest that RAC2 gene sequencing should be considered for patients with SCID clinical presentation. Disclosures Cavazzana: Smartimmune: Other: Founder of Smartimmune.

Impact of trace extrinsic defect formation on the local symmetry transition in spinel LiNi0.5Mn1.5O4−δ systems and their electrochemical characteristics

Many fundamental studies have been conducted on the electrochemical and electronic structures in transition metal cation-substituted LiNi0.5Mn1.5O4 systems.

Concentration and Annealing Effects on Luminescence Properties of Ion-Implanted Silica Layers

The development of optoelectronic or even photonic devices based on silicon technology is still a great challenge. Silicon and its oxide do not possess direct optical transitions and, therefore, are not luminescent. The remaining weak light emission is based on intrinsic and extrinsic defect luminescence. Thus the investigations are extended to ion implantation into silica layers, mainly on over-stoichiometric injection or isoelectronic substitution of both the constituents silicon or oxygen, that is, by ions of the group IV (C, Si, Ge, Sn, Pb) or the group VI (O, S, Se). The samples have been used were 500 nm thick thermally grown amorphous SiO2 layers, wet oxidized at 1100°C on a crystalline Si substrate. The ion implantations were performed with different energies but all with a uniform dose of 5 × 1016 ions/cm2. Such implantations produce new luminescence bands, partially with electronic-vibronic transitions and related multimodal spectra. Special interest should be directed to lowdimension nanocluster formation in silica layers. Implantations of group IV elements show a general increase of the luminescence in the violet-blue region and implantations of group VI elements lead to an increase in the yellow-red spectral region. Comparing cathodoluminescence, photoluminescence, and electroluminescence still too small luminescence quantum yields are obtained.

INFLUENCE OF POST-TREATMENT ON OPTICAL PROPERTIES OF Sc:Ce:Cu:LiNbO3 CRYSTALS

The congruent Sc(3 mol%):Ce:Cu:LiNbO 3 single crystals were grown by the Czochralski method and three kinds of different samples were prepared by proper reduction or oxidation post-treatment processes. The extrinsic defect structures of samples were determined by infrared transmittance spectra. Two-wave coupling and light induced scattering experiments were used to measure the photorefractive properties. It is found that the reduction treatment made erasure time and diffraction efficiency decrease, but light-induced scattering resistance increase; the inverse case occurred with oxidation treatment. Analysis indicated that photoconductivity change was responsible for photorefractive properties.